As a minimum feature size of a semiconductor device decreases, a minimum pitch size between metal lines needs to be gradually reduced. Between the metal lines, a dielectric material is inserted in order to block an unintended current path. However as the minimum pitch size decreases, an increase in line-to-line capacitance is unavoidable because of the shorter space between the metal lines. The increase in line-to-line capacitance causes an increase of RC-delay, cross-talk noise, and power dissipation, thereby deteriorating performance of the device. In order to decrease the capacitance between the metal lines, a dielectric material having a low dielectric constant should be introduced. As an example thereof, there is a carbon doped oxide (CDO) film. As rigid Si—O—Si bonds of silicon dioxide (SiO2) used in the related art are partially broken and terminal bonds such as Si—CH3 having a relatively low polarity are formed instead of the broken Si—O—Si bonds, the CDO film has a relatively low effective dielectric constant (keff). In addition, a dielectric film having a further low keff value, especially 2.4 or less, can be obtained by introducing a porosity into the CDO film, because of the lowest dielectric constant of air, which is around 1. However, the connectivity and density of the porous dielectric material decreases by introducing the porosity, such that a mechanical and chemical strength of the dielectric material significantly decreases, and moreover, the dielectric material becomes extremely vulnerable to a process-related damage. In general, pores introduced in the porous material are mutually interconnected. Therefore, plasma and chemical species, moisture, metal particles can deeply penetrate into the porous film through the mutually interconnected pores. This may result in increases of keff and leakage current of the porous material.
Therefore, a pore sealing technology is an essential technology for forming a porous low-k/ultra-low k dielectric layer in a fine pitch interconnect structure having a fine line width.
As a method known in the art, there is a densification method of a surface of a porous low-k/ultra-low k film using plasma. However, this method has a disadvantage in that plasma can cause a damage in the porous low-k/ultra-low k film to degrade the original characteristics of the film, such as increasing the dielectric constant of the film. Furthermore, in a case of increasing porosity to decrease the dielectric constant of the porous low-k/ultra-low k film, a portion of the film damaged due to the penetration of plasma species also increases.
As another method, there is a deposition method of a dense sealing layer on a surface of a porous low-k/ultra low-k dielectric material. However, this method has a disadvantage in that as a porosity of the porous low-k/ultra-low k film increases, a penetration depth of the sealing material into the film also increases. Furthermore, in some cases, it may be difficult to deposit a conformal sealing layer on a porous low-k/ultra-low k dielectric film having a trench/via structure with a high aspect ratio depending on the deposition method.
In addition to the above method, if the deposition method is based on a spin coating technology, there can be a solvent residue problem.